What does Finneas have to offer without his sister Billie Eilish?

No truth is more self-evident than that there are those whose best emerges only when they are paired with others: Lennon and McCartney, Morecambe and Wise, Clough and Taylor. And it’s perhaps even harder for a behind-the-scenes collaborator to step out in their own right.

Jack Antonoff, for example, is one of the creative powerhouses of modern pop: he co-writes and produces songs for Taylor Swift, Lana Del Rey and Lorde, who plainly regard him as intrinsic to their success. His work probably reaches more ears than any other songwriter on Earth. But when he writes and produces those songs for himself? The magic vanishes. The band he fronts, Bleachers, are popular, but no more popular than any other indie rock band that listens to Springsteen.

Ditto Finneas O’Connell, who was another not-getting-anywhere-fast musician until he got his younger sister to record a song he had written. His younger sister is Billie Eilish, and ever since he has been her creative partner as she has risen to become one of the world’s biggest stars. Listening to his set at the Fillmore — where a pint of beer is more than $19 — it was apparent that he could turn his hand to any style with ease.

There was light, twilit pop-funk, the kind of thing that should by law be produced only by the French (“What’s It Gonna Take to Break Your Heart”), chugging new wave (“Mona Lisa, Mona Lisa”), and a good bit of emotive, sarcastic balladry in the style of Father John Misty, leaning heavily on the early 1970s but with contemporary alienation layered on top. The tunes were there, but the X factor was missing. Without his sister’s sullen charisma, he was an empty jacket in search of a pair of shoulders. Compared with the actual Father John Misty, Josh Tillman, who has a remarkable voice and wields his lyrics as though they were stilettos, Finneas’s pleasant voice and blunt lyrics don’t stand a chance.

“Do you have a dollar? Would you like to fund a war?/ What’s your carbon footprint and could you be doing more?/ I tried saving the world but then I got bored,” he sang on “The Kids Are All Dying” whose sentiments are perfectly calibrated for teenagers and sound astoundingly trite to anyone older. Finneas will continue to be hugely successful and influential, but with his name in small print on the back of other people’s records.

Mdou Moctar is a guitarist from Niger backed by a three-piece band who came to attention in Europe and America when his work was featured on a compilation of tracks that had been swapped by cellphones in west Africa. Since then, he and his group have had a steady rise and have avoided being swept into the “world music” category by signing with the venerable indie label Matador.

His set at a boiling church on a freezing night in Philadelphia was breathtaking. The fact that the lyrics were in the Tamasheq language meant that I had no concerns about triteness. Moctar plays a kind of rock music known as “desert blues” — plainly not conventional rock music but played with a rock-band line up of two guitars, bass and drums, and with phrasing familiar from that great west African export, the blues. It droned and throbbed and hypnotized.

Inevitably, a group of young women felt compelled to run to the front of the stage to engage in a form of ecstatic dancing only ever reserved for artists from Africa and Asia. This admittedly brought the show to life for the front third of the church. One could feel it in the air and in the playing, which suddenly became fiery and intense. Because the band were seated on a low stage, though, it had the simultaneous effect of making the musicians invisible to anyone not in that front third, even if we all stood. Sadly, the crowd diminished notably after that. But at the front, the young women danced on, enthralled by this Tuareg Eddie Van Halen, who still sounded great, just impossible to see.